Certain forms of flexible and resilient strip material, such as venetian blind slats, have a nominally curved lateral cross section. Film strip is of that configuration with a lateral curve which is concave on an emulsion-coated side. The general field of the present invention concerns methods and apparatus for transporting such strip longitudinally through a processing station with the lateral cross section of the strip flattened.
In film strip production various procedures for developing and optically scanning the strip during production and quality control involve moving an elongated section of the strip longitudinally in a processing station with the nominally curved lateral cross section of the strip maintained substantially flat. One method of doing this is simply to press the strip between overlaying rigid plates, one or both of which may be transparent for developing or scanning purposes. Refinements include subjecting the concave side of the laterally curved strip to a vacuum to draw it down against one of the plate to augment the flattening effect of the opposed plate pressing against the convex side.
A particularly relevant prior art system is described in U.S. Pat. No. 2,479,553, which concerns motion picture film projecting apparatus for correction of spherical aberrations. This patent recognizes that film strip has a nominal lateral curve which is concave on the emulsion side, and it further recognizes the need to flatten that lateral curve as the strip is transported through a station where projection light passes through the film. The solution proposed is to advance the strip through the station by roller pairs which impose longitudinal tension on the strip and at the same time pressing the edges of the strip by means of pressure shoes against a convex curved gate having an aperture through which the projection light passes.
It is known, of course, that certain flexible resilient strip material having a nominally curved lateral cross section will collapse or snap into a substantially laterally flat cross section when the strip is bent longitudinally. Snap action devices such as bowed springs operate on that principle; see for example the bowed spring described in Mechanisms & Mechanical Devices Sourcebook by Nicholas P. Chironis, McGraw-Hill, Inc. 1991 at page 218. This snap action can be demonstrated by a push-pull type steel measuring tape which has nominal lateral curve. With the lateral curve facing concave side upward the tape can be cantilevered out a substantial distance without bending under its own weight, but when it does buckle its lateral cross section in the region of the bend becomes substantially flat.
It is a principal object of the present invention to apply this self-flattening capability of resilient strip to a strip transport system without flattening the strip between plates or subjecting it to tension or to sliding contact with pressure shoes, as in the prior art.